1. Field of the Invention
The invention relates to an electromagnetic induction sensor, an overlay member for an electromagnetic induction sensor, and a manufacturing method of an electromagnetic induction sensor.
2. Description of the Related Art
Position detecting devices of an electromagnetic induction system used with a pen-shaped position indicator have been widely used along with popularization of so-called tablet terminals, pad portable terminals, and portable information devices called personal digital assistants (PDA). Furthermore, as the thickness of these electronic apparatuses continues to be reduced, thickness of electromagnetic induction sensors used in the position detecting devices of the electromagnetic induction system is also reduced.
The electromagnetic induction sensor is electromagnetically coupled to the pen-shaped position indicator to detect a position indicated by the position indicator. For this purpose, the position indicator includes a resonant circuit composed of a coil and a capacitor to carry out the electromagnetic coupling with the sensor. The electromagnetic induction sensor includes a coil group to be electromagnetically coupled to the resonant circuit of the position indicator.
The electromagnetic induction sensor is formed of an electromagnetic sheet member called a magnetic path plate, which is adhered to a sensor board, as described in, for example, Patent Document 1 (Japanese Patent Laid-open No. 2009-3796). The electromagnetic sheet member is provided in order to allow utilization of magnetic flux generated from the sensor with as little leakage as possible in electromagnetic coupling between the sensor and a position indicator, and functions as an electromagnetic shield between the sensor and the external.
The sensor is electromagnetically coupled to the position indicator to detect a position indicated by the position indicator in the detection area where the sensor accepts an input of position indication by the position indicator. The detection area of the position indicator is set, for example, as a rectangular area and the position indicated by the position indicator is detected as two-dimensional plane coordinates of the X-axis direction (horizontal direction) and the Y-axis direction (vertical direction).
FIGS. 10A and 10B show the configuration of a related-art sensor. As shown in FIG. 10A, in a sensor board 10 configuring a sensor 1, an X-axis-direction loop coil group 12 is disposed on one surface side of an insulating substrate 11 composed of, for example, polyethylene terephthalate (PET), and a Y-axis-direction loop coil group 13 is disposed on the other surface side. Furthermore, in the example of FIG. 10A, for the sensor board 10, a surface sheet (overlay) 14 formed of, for example, a PET film is so formed as to cover the entirety of the X-axis-direction loop coil group 12, and a protective sheet (overlay) 15 is so formed as to cover the entirety of the Y-axis-direction loop coil group 13.
The overlay is a layer of an insulating material used to wholly or partially wrap and cover a conductor pattern formed on the external surface of a printed wiring board such as the sensor board 10 (See “Denshi Kairo Yougo (Electronic Circuit Terms and Definition)” JPCA-TD01-2008 Japan Electronics Packaging Circuits Association). In the present specification, a member that is or includes an overlay and is integrally joined to (or formed with) a sensor board (a main body of a sensor board, to be described later) to thereby form a sensor will be referred to as an overlay member.
The overlay member configuring the surface sheet 14 and the overlay member configuring the protective sheet 15 are formed by applying an adhesive (not shown) on one surface side of a PET film as the insulating material, for example. Via the adhesive, the overlay members (formed of a PET film, for example) are so adhered to the sensor board 10 as to cover each of the X-axis-direction loop coil group 12 and the Y-axis-direction loop coil group 13. The sensor board 10 is completed when the surface sheet 14 and the protective sheet 15 formed as the overlay members are attached. In this example, a position indicator is so configured that a position indication input is made to the sensor board 10 from the side of the surface sheet 14.
As shown in FIG. 10B, an electromagnetic sheet member 2 called a magnetic path plate includes a first layer 21 forming a magnetic path material and a second layer 22 for electromagnetic shielding. The first layer 21 forming the magnetic path material provides a magnetic path for an alternating magnetic field generated by a loop coil of the loop coil group 12 or 13 in connection with transmission and reception of electromagnetic waves, to thereby prevent diversion of the generated magnetic flux and to enhance the detection sensitivity of the electromagnetic induction sensor 1 regarding the position indicator. The second layer 22 for electromagnetic shielding performs a function to prevent an alternating magnetic field from being radiated to the external toward the side of the protective sheet 15 of the electromagnetic induction sensor 1, and also to prevent electromagnetic waves from the external on the protective sheet 15 side from mixing, as noise, into electromagnetic waves transmitted and received on the side of the surface sheet 14.
As the first layer 21, a layer having high magnetic permeability is used. Specifically, in related arts, magnetic iron plates such as a permalloy plate and a silicon steel plate are used pursuant to recent demands to reduce thickness of the electromagnetic induction sensors. In particular, recently, an amorphous alloy that has permeability as high as, for example, 1000 (H/m) and can be thinned to a thickness as small as, for example, 25 microns is used as the first layer 21 of the magnetic path material. The second layer 22 is formed of a metal material that is a non-magnetic material and has high electrical conductivity, for example, aluminum.
Because the amorphous alloy has extremely low electrical resistance, an eddy current is generated therein due to the magnetic flux applied to the magnetic path material formed as the first layer 21. The eddy current acts to cancel the applied magnetic field. Even considering the disadvantage associated with the generation of the eddy current, all in all the amorphous alloy having high permeability is considered as a high-performance magnetic path plate. Therefore, the amorphous alloy has been used as the magnetic path material to form the first layer 21 thus far.
The electromagnetic sheet member 2 is formed by adhering an aluminum layer as the second layer 22 to a PET film 23 serving as a protective layer, and forming the first layer 21 composed of an amorphous alloy on the second layer 22 composed of aluminum. Furthermore, in the electromagnetic sheet member 2, an adhesive layer 24 is applied on the first layer 21 composed of the amorphous alloy.
The adhesive layer 24 of the electromagnetic sheet member 2 is bonded to the protective sheet 15 of the sensor board 10. Then, as shown in FIG. 11, the electromagnetic sheet member 2 is adhered to the sensor board 10, so that the electromagnetic induction sensor 1 is formed. In this manner, in the related art, the sensor board 10 and the electromagnetic sheet member 2 are separately formed independent of each other and are adhered to each other, to thereby form the electromagnetic induction sensor 1.